



 
First, the picture. "Meridian" comes from the word for "noon"  it's a line of places that all have solar noon at once, that is, a northsouth line, a line of constant longitude. As a result, they are all the same length  unlike "parallels", lines of constant latitide, which get smaller as you approach the poles. And that common length is the length of a great circle. it would help to have the same units. So how many km is 270 miles? If the Earth has radius 6380 km, what is its circumference? [You should get a surprisingly round number. Look up the history of the meter to see why. There are 360 degrees in a circle: how many kilometers to a longitudinal degree? Good hunting!  


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